fetch-pack: test explicitly that --all can fetch tag references pointing to non-commits

Fetch-pack --all became broken with respect to unusual tags in
5f0fc64 (fetch-pack: eliminate spurious error messages, 2012-09-09),
and was fixed only recently in e9502c0 (fetch-pack: don't try to fetch
peel values with --all, 2018-06-11). However the test added in
e9502c0 does not explicitly cover all funky cases.

In order to be sure fetching funky tags will never break, let's
explicitly test all relevant cases with 4 tag objects pointing to 1) a
blob, 2) a tree, 3) a commit, and 4) another tag objects. The referenced
tag objects themselves are referenced from under regular refs/tags/*
namespace. Before e9502c0 `fetch-pack --all` was failing e.g. this way:

        .../git/t/trash directory.t5500-fetch-pack/fetchall$ git ls-remote ..
        44085874...        HEAD
        ...
        bc4e9e1f...        refs/tags/tag-to-blob
        038f48ad...        refs/tags/tag-to-blob^{}	# peeled
        520db1f5...        refs/tags/tag-to-tree
        7395c100...        refs/tags/tag-to-tree^{}	# peeled

        .../git/t/trash directory.t5500-fetch-pack/fetchall$ git fetch-pack --all ..
        fatal: A git upload-pack: not our ref 038f48ad...
        fatal: The remote end hung up unexpectedly

Helped-by: Junio C Hamano <gitster@pobox.com>
Signed-off-by: Kirill Smelkov <kirr@nexedi.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: navytux

t/t5500-fetch-pack.sh

@@ -528,6 +528,37 @@ test_expect_success 'test --all with tag to non-tip' '
 	)
 '
 
+test_expect_success 'test --all wrt tag to non-commits' '
+	# create tag-to-{blob,tree,commit,tag}, making sure all tagged objects
+	# are reachable only via created tag references.
+	blob=$(echo "hello blob" | git hash-object -t blob -w --stdin) &&
+	git tag -a -m "tag -> blob" tag-to-blob $blob &&
+ \
+	tree=$(printf "100644 blob $blob\tfile" | git mktree) &&
+	git tag -a -m "tag -> tree" tag-to-tree $tree &&
+ \
+	tree2=$(printf "100644 blob $blob\tfile2" | git mktree) &&
+	commit=$(git commit-tree -m "hello commit" $tree) &&
+	git tag -a -m "tag -> commit" tag-to-commit $commit &&
+ \
+	blob2=$(echo "hello blob2" | git hash-object -t blob -w --stdin) &&
+	tag=$(printf "object $blob2\ntype blob\ntag tag-to-blob2\n\
+tagger author A U Thor <author@example.com> 0 +0000\n\nhello tag" | git mktag) &&
+	git tag -a -m "tag -> tag" tag-to-tag $tag &&
+ \
+	# `fetch-pack --all` should succeed fetching all those objects.
+	mkdir fetchall &&
+	(
+		cd fetchall &&
+		git init &&
+		git fetch-pack --all .. &&
+		git cat-file blob $blob >/dev/null &&
+		git cat-file tree $tree >/dev/null &&
+		git cat-file commit $commit >/dev/null &&
+		git cat-file tag $tag >/dev/null
+	)
+'
+
 test_expect_success 'shallow fetch with tags does not break the repository' '
 	mkdir repo1 &&
 	(